Inhaled nitric oxide fraction is influenced by both the site and the mode of administration

Objective. Inhaled nitric oxide (NO) can be delivered continuously or seque ntially (= during inspiration) at different locations of the ventilation ci rcuit. We have tested the influence of locations, modes of NO administratio n and the ratio of the inspiratory time over the respiratory cycle time (I/ I + E ratio) on the accuracy of NO fractions, delivered by 2 devices: Opti- NO and Flowmeter. Methods. We used a simplified lung model consisting of a ventilation circuit with a Y piece, a tracheal tube, a 150 ml dead-space vo lume and a 5 liter balloon. Three fractions (3, 6, 9 ppm) were administered continuously or sequentially, in controlled volume, in 4 different sites o n the inspiratory branch above the Y piece: i) just after the water trap, i i) just before the Y piece; below the Y piece:iii) just after the Y piece, iv) into the endotracheal tube. In addition, different I/I + E ratios (25, 33, 50, 80%) were studied. The delivered NO fractions were measured in the balloon by chemiluminescence (CLD 700, Ecophysics). A linear regression ana lysis was used to test the relationship between administered and measured N O fractions for the 3 fractions (3, 6 and 9 ppm) in sequential and continuo us modes. Intercept values were compared to zero and slopes to the identity line. Results. When NO was administered in the continuous mode upstream th e Y piece, NO fractions measured in the balloon corresponded to the adminis tered fractions. In contrast, below the Y piece, the measured NO fractions were significantly lower than the administered NO fractions. In the sequent ial mode, above and below the Y piece, the delivered NO fractions were with in the manufacturer's range. Conclusions. For the continuous NO delivery, l ocations above the Y piece are mandatory. However, locations below the Y pi ece imposes a sequential system, which can also be used for the sites locat ed above the Y piece.